This invention relates to an intestinal tissue covered prosthesis useful in promoting the resurfacing and repair of damaged or diseased tissue structures. More particularly this invention is directed to stents having a layer of submucosal tissue covering a surface of the stent, and their use in repairing damaged or diseased physiological vessels, particularly blood vessels.
The most common cause of vascular disease in the Western world is atherosclerosis, in which cholesterol and fibrous tissue, often together with calcium precipitates, gradually build up within the inner layers of the arterial wall, diminishing the cross sectional area available for blood flow. There are two essential abnormalities of such atherosclerotic lesions that cause complications. The first is the narrowing of the lumen, which produces a chronic limitation of blood flow distally. The second is the abnormally raised, roughened inner surface of the artery, the physical properties of which tend to induce platelet adhesion and clot formation at the diseased site. Thrombosis can produce sudden cessation of blood flow with disastrous consequences for downstream organs such as the brain, heart muscle, kidney, or lower extremities. The eroded, abnormal intimal surface of sclerotic vessels causes additional complications including fragmentation of atherosclerotic material with downstream embolization and hemorrhage or dissection of blood into the plaque itself causing sudden expansion of the lesion and occlusion of the vessel.
Percutaneous transluminal angioplasty (PTA), first performed 25 years ago by Dotter and Judkins, is the technique of opening narrowed or occluded blood vessels by passing guide wires and catheters through the stenotic or occluded portion of the blood vessel. Dotter""s original PTA method involved inserting increasingly larger catheters over a guidewire to progressively dilate the vessel. Later modifications utilized graduated catheters with gradually tapering tips, which created more lateral compression and less longitudinal shearing action. These early PTA procedures were limited by the requisite stiffness of the catheters and by the large puncture wounds required for the procedure.
In 1974, PTA procedures were revolutionized by the introduction of balloon catheter angioplasty. A balloon catheter has an expandable sac that can be expanded and contracted in a controlled manner in response to inflation pressure. Balloon catheter angioplasty involves positioning the balloon catheter at a stenotic site and inflating the sac to a predetermined size to open the stenotic or occluded portion of the blood vessel. The sac is then deflated and the catheter removed leaving a larger lumen. Standard balloon angioplasty, with or without the use of stents, produces a torn vessel with myointimal flaps and exposed fissures. These provide thrombogenic surfaces and sites for hemodynamic dissection. Furthermore, although the use of the stents in PTA procedures gives highly predictable immediate angiographic results, those stents all suffer the disadvantage that they have limited long term efficacy. Despite holding the vessel open, the natural reparative processes at a stent-dilated vessel result in healing tissues growing around the stent structure and eventually occluding the lumen of the vessel. In addition to PTA procedures, alternative techniques for removing atherosclerotic plaques include laser angioplasty and mechanical arthrectomy devices, which can vaporize, melt, or remove plaque material. However all such systems leave an abnormal, thrombogenic surface.
Angioplasty is now known to damage the vessel wall by tearing and stretching, and this form of controlled injury opens the vessel lumen and increases blood flow acutely in nearly all cases. However, abrupt vessel closure during or immediately following PTA and late restenosis continues to limit the effectiveness of the procedure. To enhance the efficacy of PTA procedures catheters have been fitted with vascular stents.
Stents are three dimensional implantable structures that (upon delivery to an intra vessel position) physically hold a blood vessel open. Vascular stents are typically formed to fit on the end of conventional catheters for delivery of the stent to a predetermined intravascular location. A number of stents for coronary use are commercially available. They differ in physicochemical characteristics and the mode of implantation. Ideally, a stent should be flexible, thrombo-resistant, low in profile, radiopaque, limit the expansion of repair tissues into the lumen of the vessel, and have an easy, reliable delivery system. Currently available expandable stents can be categorized as xe2x80x9cself expandable stentsxe2x80x9d and xe2x80x9cballoon expandable stents.xe2x80x9d Self-expanding stents utilize a spring mechanism to constrain the stent to a compressed shape. Upon removal of the constraint, the stent expands to a predetermined dimension. Balloon expandable stents are expandable members formed to fit over a balloon catheter and capable of being expanded in response to controlled inflation of the balloon catheter. Inflation of the balloon results in plastic deformation of the stent beyond its elastic limits so that the stent remains in its expanded state upon subsequent deflation and removal of the balloon catheter. Preferably stents used in conjunction with PTA are xe2x80x9cexpandable stentsxe2x80x9d having an initial collapsed state that allows the stent to be delivered to the desired intravascular location with minimal longitudinal shearing action. Upon delivery to the desired location the stent is expanded to fix the stent at that location and to physically hold the vessel open.
The present invention utilizes a natural collagenous matrix comprising submucosal tissue in combination with known angioplastic techniques to eliminate complications that derive from the residual abnormal, thrombogenic surfaces produced by current available angioplastic techniques such as ordinary balloon angioplasty, laser angioplasty, and transluminal mechanical arthrectomy. The collagenous matrices for use in accordance with the present invention comprise highly conserved collagens, glycoproteins, proteoglycans, and glycosaminoglycans in their natural configuration and natural concentration. One preferred collagenous matrix comprises warm-blooded vertebrate submucosa.
In accordance with the present invention the submucosa is isolated from warm-blooded vertebrate tissues including the alimentary, respiratory, intestinal, urinary or genital tracts of warm-blooded vertebrates. The preparation of intestinal submucosa is described and claimed in U.S. Pat. No. 4,902,508, the disclosure of which is expressly incorporated herein by reference. Urinary bladder submucosa and its preparation is described in U.S. Pat. No. 5,554,389, the disclosure of which is expressly incorporated herein by reference. Stomach submucosa has also been obtained and characterized using similar tissue processing techniques. Such is described in U.S. patent application No. 60/032,683 titled STOMACH SUBMUCOSA DERIVED TISSUE GRAFT, filed on Dec. 10, 1996. Briefly, stomach submucosa is prepared from a segment of stomach in a procedure similar to the preparation of intestinal submucosa. A segment of stomach tissue is first subjected to abrasion using a longitudinal wiping motion to remove the outer layers (particularly the smooth muscle layers) and the luminal portions of the tunica musoca layers. The resulting submucosa tissue has a thickness of about 100 to about 200 micrometers, and consists primarily (greater than 98%) of acellular, eosinophilic staining (HandE stain) extracellular matrix material.
Preferred submucosal tissues for use in accordance with this invention include intestinal submucosa, stomach submucosa, urinary bladder submucosa, and uterine submucosa. Intestinal submucosal tissue is one preferred starting material, and more particularly intestinal submucosa delaminated from both the tunica muscularis and at least the tunica mucosa of warm-blooded vertebrate intestine.
As a tissue graft, submucosal tissue undergoes remodeling and induces the growth of endogenous tissues upon implantation into a host. It has been used successfully in vascular grafts, urinary bladder and hernia repair, replacement and repair of tendons and ligaments, and dermal grafts. The preparation and use of submucosa as a tissue graft composition is described in U.S. Pat. Nos. 4,902,508; 5,281,422; 5,275,826; 5,554,389; and other related U.S. patents. When used in such applications the graft constructs appear not only to serve as a matrix for the regrowth of the tissues replaced by the graft constructs, but also promote or induce such regrowth of endogenous tissue. Common events to this remodeling process include: widespread and very rapid neovascularization, proliferation of granulation mesenchymal cells, biodegradation/resorption of implanted intestinal submucosal tissue material, and lack of immune rejection. The use of submucosal tissue in sheet form and fluidized forms for inducing the formation of endogenous tissues is described and claimed in U.S. Pat. Nos. 5,281,422 and 5,275,826, the disclosures of which are expressly incorporated herein by reference.
The present invention is directed to an improved prosthetic device for repairing the intimal surface of damaged or diseased vessels. The prosthetic devices of the present invention can also be used in traditional PTA procedures to open narrowed or occluded vessels. In one embodiment the prosthetic device comprises a cylindrical shaped expandable member having a luminal and exterior surface, and a layer of submucosal tissue fixed to the exterior or luminal surface of the member. The expandable member is typically a stent wherein expansion of the stent increases the circumference of said member, thus fixing the device at a predetermined location within the vessel.